The present invention relates to a data conversion technique, and signal recording and reproduction apparatus for format conversion of compressed encoded data and, more particularly, to a data conversion technique for data conversion between first-format encoded data in which orthogonal transform coefficients are arranged in an order of DC components and AC components from a low spatial frequency order to a high spatial frequency order in each orthogonal transform block when compression encoding which includes orthogonal transform is applied to video data and second-format encoded data in which orthogonal transform coefficients are arranged in an order of DC components and AC components from a low spatial frequency order to a high spatial frequency order in each block assembly member in which a plurality of orthogonal transform blocks are grouped when compression encoding which includes orthogonal transform is applied to video data, and to a signal recording and reproduction apparatus utilizing such data conversion technique.
Several types of formats for recording a digital video signal on a recording medium and transmitting the same may be utilized. Since a digital video signal generally has a relatively large amount of data, such signal may be subjected to compression encoding so as to enable data corresponding to a relatively long period of record/playback time to be recorded on a recording medium. An example of such compression encoding method is a so-called MPEG (Moving Picture Image Coding Experts Group) method which is discussed in ISO-IEC/JTC1/SC2/WG11 and proposed as a standard method. Such method is a hybrid method in which motion-compensation predictive coding and discrete cosine transform (DCT) coding are combined. In the MPEG method, redundancy in the time domain may be reduced by use of the difference between frames of a video signal and redundancy in the spatial domain may be reduced by the use of discrete cosine transform to efficiently encode the video signal.
In a video tape recorder (VTR) which uses a tape-type medium such as magnetic tape as a recording medium, recording may be performed such that tracks disposed at an angle to a tape running direction (so-called helical tracks) are formed with the use of a rotating head. When a tape-type recording medium having such helical tracks is reproduced at a tape running speed higher than a normal running speed, such as double or triple speed or as in a search function, the trace angle of the rotating head on the tape may be different from the angle of the recording tracks. As a result, all signals recorded in the helical tracks may not be reproduced. In other words, only a part of each helical track may be scanned (traced) in high-speed reproduction.
Therefore, if the MPEG method is used to compression encode data recovered in a tape-type recording medium and if such data is reproduced during a high speed reproduction operation (such as a search function), a high-quality reproduced image may not be obtained due to the above-described tracing of only a part of each helical track.
Accordingly, it may be desirable to have a compression encoding method for use in encoding data for recording on a tape-type recording medium which enables image reproduction to be performed somewhat effectively even in high-speed reproduction.
A recording format for a compression encoding method may be utilized in which all DC coefficients and AC coefficients of lower spatial frequency important for image reproduction in a macroblock can be read out in a high-speed reproduction (such as in a search function) by grouping the DC coefficients of all DCT blocks in the macroblock and by grouping the AC coefficients of all the DCT blocks in order of their spatial frequency and sequentially arranging them. However, such a format may be primarily intended for use with a professional broadcasting VTR or the like. In addition, it may be preferred that encoded data having a standard format, such as an MPEG standard, be used for data transmission with other units.
Further, encoded data having a format suited for VTR recording may be decoded to obtain the original non-compressed video data and compression encoding may be applied to it with a standard format such as that of MPEG. Such arrangement, however, may utilize a relatively large circuit and a relatively large amount of processing.
An object of the present invention is to provide a data conversion technique adaptable for use in a signal recording and reproduction apparatus which enables conversion from encoded data having a format suitable for VTR recording and reproduction to encoded data having a standard format such as MPEG which may be implemented in a relatively small circuit and utilize a relatively small amount of processing.
In accordance with an aspect of the present invention, a data conversion apparatus is provided for performing data conversion between first-format encoded data in which orthogonal transform coefficients are arranged in an order of DC components and AC components from a low spatial frequency order to a high spatial frequency order in each orthogonal transform block when compression encoding which includes orthogonal transform is applied to video data and second-format encoded data in which orthogonal transform coefficients are arranged in an order of DC components and AC components from a low spatial frequency order to a high spatial frequency order in each block assembly member formed of a plurality of orthogonal transform blocks when compression encoding which includes orthogonal transform is applied to video data. Such apparatus includes a decoding device for decoding the second-format encoded data to obtain orthogonal transform coefficients; a conversion device for re-arranging the orthogonal transform coefficients of the second-format data obtained by the decoding device in the order of the DC components and AC components from a low spatial frequency order to a high spatial frequency order in each orthogonal transform block of the first format; and an encoding device for encoding the orthogonal transform coefficients from the conversion device to form encoded data having the first format.
The data conversion apparatus may be formed such that the orthogonal transform is discrete cosine transform (DCT), the orthogonal transform block is a DCT block, and the block assembly member is a macroblock. The data conversion apparatus may further be formed such that the decoding device is a variable-length decoding device, and the encoding device is a variable-length encoding device.
According to another aspect of the present invention, a signal recording and reproduction apparatus is provided for recording and reproducing into and from a recording medium encoded data having a second format in which orthogonal transform coefficients are arranged in an order of DC components and AC components from a low spatial frequency order to a high spatial frequency order in each block assembly member formed of a plurality of orthogonal transform blocks when compression encoding which includes orthogonal transform is applied to video data. Such apparatus includes a decoding device for decoding the encoded data having the second format reproduced from the recording medium to obtain orthogonal transform coefficients; a conversion device for re-arranging the orthogonal transform coefficients of the second-format data obtained by the decoding device to the coefficient arrangement order of a first format in which the coefficients are arranged in the order of the DC components and AC components from a low spatial frequency order to a high spatial frequency order in each orthogonal transform block; and an encoding device for encoding the orthogonal transform coefficients from the conversion device to form encoded data having the first format.
Partial decoding may be applied to obtain orthogonal transform coefficients, the orthogonal transform coefficients may be re-arranged without applying reverse orthogonal transform, and partial encoding corresponding to the partial decoding may be applied. With the use of only these operations, encoded data having the second format can be converted to encoded data having the first format.
Other objects, features and advantages according to the present invention will become apparent from the following detailed description of illustrated embodiments when read in conjunction with the accompanying drawings in which corresponding components are identified by the same reference numerals.